Handler.cs

public class GetMyOrdersHandler : IRequestHandler<GetMyOrdersQuery, GetMyOrdersViewModel>
{
    private readonly CatalogContext _db;

    public GetMyOrdersHandler(CatalogContext db)
    {
        _db = db;
    }

    public async Task<GetMyOrdersViewModel> Handle(GetMyOrdersQuery request, CancellationToken cancellationToken)
    {
        var result = new GetMyOrdersViewModel();

        result.Orders = await _db.CustomerOrdersWithItems(request.UserName)
            .Select(o => new OrderSummaryViewModel
            {
                OrderDate = o.OrderDate,
                OrderNumber = o.Id,
                Total = o.OrderItems.Sum(x => x.Units * x.UnitPrice),
            })
            .ToArrayAsync(cancellationToken);

        return result;
    }
}